A thin film transistor liquid crystal display (TFT-LCD) has characteristics such as small size, low consumption, no radiation and the like, and has prevailed in the current market of the flat panel display. Amorphous silicon (a-Si) becomes the most widely used active layer material in TFT-LCDs since it is easy to be prepared in a large area under a low temperature with mature technologies. However, the amorphous silicon material has a band gap of only 1.7V, is not transparent to visible light, and has the light sensitivity within the range of visible light, thus a black matrix is needed to block light. This increases the complexity of the process for TFT-LCDs, enhances costs and decreases the reliability and the aperture ratio of displays.
In addition, with the constant increase of the sizes of liquid crystal displays, the frequencies of the drive circuits required are improved constantly. The mobility of the amorphous silicon thin film transistor is usually about 0.5 cm2/VS. However, when the size of a liquid crystal display is beyond 80 inches, its driving frequency is beyond 120 Hz, and the thin film transistors require mobility over 1 cm2/VS, and therefore the mobility of the existing amorphous silicon thin film transistors are hard to meet the requirement.
Oxide semiconductor thin film transistors are favored by researchers, possess many advantages and are improved fast in recent years. An oxide semiconductor has a high mobility, good uniformity and transparency, and can better meet the requirements for driving a liquid crystal display of a large size and an OLED. However, the existing oxide semiconductor thin film transistor is formed with at least four patterning processes when it is in a bottom-gate type, and protection provided with an etching stop layer (ESL), a passivation layer (PVX) and the like is needed to ensure the stability of the thin film crystal, and therefore the process is complex and the manufacture costs are high.